1. Field of the Invention
The present invention concerns an operating method for a magnetic resonance system of the type having a number of individual transmission antennas that can be each be charged with a transmission current, by means of multiple individual excitation fields are respectively generated in an examination volume of the magnetic resonance examination system to excite magnetic resonances and, due to the superimposition of the individual excitation fields, overall a total excitation field is generated to excite magnetic resonances, wherein the control device charges the transmission antennas with transmission currents.
Furthermore, the present invention concerns an operating program, wherein the operating program encoded with programming instructions that can be executed by a determination device connected to a control device of a magnetic resonance system.
The present invention furthermore concerns a determination device connected to the control device of a magnetic resonance system, the determination device being programmed with such an operating program.
The present invention also concerns a magnetic resonance system that has a number of transmission antennas, an examination volume and a control device, wherein the transmission antennas and the control device interact in operation of the magnetic resonance system.
2. Description of the Prior Art
The basic operation of the items noted above is generally known.
To excite nuclear spins in an examination subject (often a person) to cause emission of magnetic resonance signals from the subject, it is necessary to expose the examination subject to a relatively strong, static magnetic field (basic magnetic field) and then to excite the examination subject (by means of radio-frequency excitation pulses) to emit magnetic resonance signals. It is known that the excitation pulses can hereby be generated by means of a number of transmission antennas. The transmission antennas can be individually charged with transmission currents for this purpose.
The individual excitation fields emitted by the transmission antennas and superimposed into a total excitation field are partially absorbed by the examination subject. The absorption leads to heating of the examination subject. Excessively high power absorption can burn the examination subject or is perceived by the examination subject as subjectively uncomfortable. The amplitudes and the phase positions of the transmission currents therefore must be determined so that the power locally absorbed by the examination subject is not too high at any point of the examination subject.
In the prior art, the amplitudes and the phase positions of the transmission currents are conservatively determined. An estimation ensues such that the maximum of the locally absorbed power is with certainty below a maximum allowable value.